The hip injury sustained by Robin Van Persie in Manchester United’s 2-0 win over QPR could not have come at a worse time for Sir Alex Ferguson. It is doubtful as to whether his star striker will be fully fit ahead of a tough run of games including Real Madrid in the Champions League and an FA Cup Quarter-Final against Chelsea.

The United manager will be well aware he may have to chop and change if Van Persie is carrying a knock for these encounters. Two games that will determine just how serious United are about going after another historic treble.

For a player like Van Persie who was so often besieged by injury problems in his time at Arsenal, this day was always going to come for Manchester United. Alex Ferguson, being as studious a football man as he is, will have already considered his options if Van Persie could not feature. Probably long, long before the QPR game.

Phil Jones is another doubt for the Real Madrid clash. If the Red Devils were to take to the field without Jones and Van Persie, then that would be a major blow, as both were significant in United coming away from the Bernabeu with a 1-1 draw. Jones helped minimise Ronaldo’s influence, whilst Van Persie offered an outlet, creating a host of chances with his wonderful touch and clever movement.

Without Van Persie and Jones, United could start afresh from a tactical point of view. Either that or two players must step into like-for-like roles.

Do United have anyone capable of filling the void left by Van Persie or Jones? Or will Ferguson clear his tactics board and devise a whole new game-plan? Just as he has done many, many times before.

Lets have a look at how the potential omissions of Jones and Van Persie will effect the Manchester United team in the coming weeks...

Increased Responsibility for Rooney

Clive Mason/Getty ImagesRooney might have to go from goal-provider to goalscorer

In the first leg at the Bernabeu, Wayne Rooney did a job for the team.

Playing on the right of midfield in a 4-4-1-1 formation, he was part of a three-pronged effort at stopping Ronaldo. Rafael and Jones also contributed to help minimise the efforts of the Portuguese forward.

With Van Persie missing, Rooney is United’s most senior striker. For that reason, Ferguson might choose Rooney to lead the line in the upcoming fixtures. Against Madrid in particular, United look as though they will have to score at least once in order to progress. Well, that is if Real’s 3-1 win in the Nou Camp is anything to go by.

Would Ferguson really trust Danny Welbeck or Javier Hernandez to lead the line in such a high-pressure game? Possibly not. Especially not over Rooney, who has done it in big games gone before. His experience will be key.

Rooney has operated at the forefront of the attack many times for Manchester United down the years. Especially in encounters like this.

He is no stranger to the role, and If United are going to look at attacking Madrid at Old Trafford—and if Van Persie is absent—then Rooney should be the man to lead the charge.

The Real Madrid defence did not cope well with Van Persie in the first leg. Raphael Varane, Sergio Ramos and Pepe are comfortable with physical battles and are quick across the ground, but they all can be bamboozled by intelligent forwards like Van Persie and potentially Rooney. That is an area in which Alex Ferguson might feel as though Rooney can hurt Madrid.

Welbeck or Hernandez?

Michael Regan/Getty ImagesHernandez and Welbeck should get a start each in United's two crunch encounters

It is all well and good trying to attack Real Madrid, but they have displayed on a multitude of occasions this season just how good they are on the counterattack. If United push up and leave space for Angel Di Maria and, particularly, Cristiano Ronaldo, then they could find themselves in a heap of trouble.

This is one of the reasons why Ferguson is more likely to play Rooney up top against Chelsea as opposed to Real Madrid. He witnessed firsthand at the Nou Camp what Real Madrid are capable of when teams come at them. Both of Ronaldo’s goals came from Barcelona being left short in wide areas and pushed high up pitch. If Rooney plays on one of the flanks, then United will give up less space due to his excellent work rate.

With Rooney operating wide, this will leave a striking berth open for either Danny Welbeck or Chicharito. The United manager chose to go with Welbeck in the Bernabeu. But as was the case with Rooney, Welbeck was also used on the flank to try and counter the threat Madrid pose in those areas.

Expect Welbeck to start again against Real Madrid. Hernandez is undoubtedly the superior goalscorer, but Welbeck offers a better all-round package, which will be key in a contest in which United may not see as much of the ball as they usually would at Old Trafford.

Welbeck also brings much more flexibility as he is capable of operating anywhere along the forward line.

Whether Ferguson choses Welbeck or Rooney to spearhead the attack remains to be seen, but one will definitely operate from a wide area.

That would leave Chicharito to start against Chelsea in place of Welbeck.

Chelsea are side whom Hernandez has fared well against in recent encounters. His movement and running in-behind have caused Chelsea’s defence no end of problems in the two previous encounters between the sides this season. The Mexican has already bagged two goals against Chelsea this campaign.

Legs in the Middle or on the Wing? What About Neither?

Ian Walton/Getty ImagesDoes Anderson have the energy to step in for Phil Jones?

As I have already alluded to, the reasons as to why Rooney and Welbeck started in wide positions at the Bernabeu is due to their work rate. Work rate that is far superior to that of Antonio Valencia, Ashley Young or Nani.

But with one of the aforementioned England strikers likely to operate as a centre-forward in the return leg and with Phil Jones potentially out of the side, United might have a problem. They will be depleted in terms of work rate on the wing and in the central midfield area. With Jones and Van Persie out, that is without question.

So from his squad of players, the Manchester United manager must have to find some willing runners to compensate. It has to be said, the options are somewhat scarce—particularly in central midfield.

If Van Persie doesn't feature against Madrid, expect Antonio Valencia to come into the side. He has been out of form as of late, but he has a good engine and some experience in defensive positions, having featured at right-back earlier in the season. He should be able to do a good job defensively whilst posing an attacking threat too.

Looking for a replacement for Phil Jones probably represents Ferguson’s toughest task ahead of the Madrid game. His first port of call would have usually been Darren Fletcher, but his long-term issues see him a fair way away from featuring. Neither Ryan Giggs nor Paul Scholes have the physicality to get about the pitch in the way Jones does, whilst Tom Cleverley is more of a playmaker than a destroyer.

The only player who might have the physicality to do the job is Anderson. He has a good engine, is pacey and can get about the pitch. His defensive work is lacking considerably in comparison to that of Jones, however, so I cannot see Ferguson trusting him in a game of this magnitude.

Instead, put bluntly, Ferguson might just go for it.

United were outscoring teams earlier on this campaign and with no outstanding candidate to step in for Jones, it could well be that Ferguson abandons the cautious approach that was evident in the first leg.

Giggs or Cleverley could come into the central midfield position and contribute towards an attacking assault on Madrid.

A gamble? With Madrid’s firepower and counterattacking nous, absolutely. But does Ferguson really have any other alternative if Jones is missing from the midfield? It would certainly represent the most exciting option for neutrals looking on.

How to Use Kagawa

Jasper Juinen/Getty ImagesKagawa failed to make an impression at the Bernabeu

Shinji Kagawa is clearly a player that Alex Ferguson has high hopes for.

But after an impressive debut at Everton in the season opener, it's not really gone well for the Japanese international. Loss of form and fitness have contributed to a frustrating season for the ex-Dortmund man.

But despite all of that, Kagawa has still featured in some big fixtures for United this season, and he will be looking to get his fitness up to speed by playing in as many of the upcoming games as possible.

The problem with Kagawa is that he has yet to find a settled position in the United side. He was so effective at Dortmund as the No.10 in a 4-2-3-1 system, but he has struggled as the No.10 in United's 4-4-1-1 system. The Japanese often finds himself without support due to Van Persie's running in-behind and the wide players not being in close proximity. He has yet to fare much better recently, having been pushed into wide areas on occasion.

In the Bernabeu, Kagawa was probably United's most disappointing performer. Does Ferguson use him in the return leg?

Not for me. Kagawa will come good eventually, but at the moment he is not dynamic enough to pose a threat to a Madrid midfield and defence packed with supreme athletes. In the first leg he found himself in a lot of good positions before dallying in possession and being dispossessed by either Sami Khedira or Xabi Alonso.

With Madrid likely to sit deep and spring into action quickly following turnovers in play, Kagawa would have even less space to operate in.

I failed to see anything from the first encounter that suggests Kagawa is the man who can help United break down a deep-sitting defence. However, If United need a goal late on, he would be a good option to come off the bench against a tiring Madrid defence.